1. Field of Invention
The present invention is related to semiconductor fabrication. More particularly, the invention is related to plasma processing during semiconductor fabrication.
2. Description of Related Art
In the fabrication of semiconductor based devices (e.g. integrated circuits or flat panel displays) layers of material may alternately be deposited onto and etched from a workpiece surface (e.g., the semiconductor wafer or the glass panel). As is well known in the art, the etching of the deposited layer(s) may be accomplished by a variety of techniques, including plasma-enhanced etching. In plasma-enhanced etching, the actual etching of the workpiece takes place inside a plasma processing chamber. During the etching process, a plasma is formed from a suitable etchant source gas to etch areas of the workpiece that are unprotected by the mask, leaving behind the desired pattern.
There are two types of plasmas that are employed in plasma-enhanced etching, namely, confined plasmas and unconfined plasmas. Unconfined plasmas touch the plasma processing chamber walls and may contaminate the workpiece by re-depositing atoms from the chamber walls on to the workpiece. Typically, the plasma processing chamber walls are made of materials that are incompatible to the workpiece. With confined plasma, there is little or no contamination since the plasma is stopped by some means from reaching the chamber walls. Thus, confined plasmas provide a level of cleanliness that is not provided by well-known unconfined plasmas.
Generating confined plasma may prove, however, difficult since it has a high electric potential with respect to the chamber walls. This high potential in connection with a given geometry of the reactor and gas pressure outside the confinement means can lead to electric breakdown of the gas and the ignition of plasma outside the confined region. Furthermore, large RF return currents on the inner surface of the chamber walls may inductively couple RF energy into the gas outside the confinement means. This may also lead to electric breakdown of the gas and, therefore, will enable the plasma to spread to the chamber walls. This undesirable state will be referred to as unconfinement.
Typically, plasma can be prevented from reaching the chamber walls by establishing a variety of repulsive fields, either electric or magnetic in nature. By way of example, the plasma is confined by a plurality of confinement rings resident within the chamber walls and by means of draining charge out of the plasma just before it can reach the inner limits of the confinement rings. Since the confinement rings are made from an insulating material they will charge to a potential comparable to that of the plasma. Consequently, a repulsive electric field will emanate from the leading edge of each confinement ring that will keep plasma from protruding any further out toward the chamber walls.
Among the different types of plasma etching systems, those utilizing confinement rings have proven to be highly suitable and effective for the production of semiconductors. An example of such a system may be found in commonly assigned U.S. Pat. No. 5,534,751 and U.S. Pat. No. 6,019,060 which are hereby incorporated by reference.
The Lenz et al. U.S. Pat. No. 5,534,751 disclosure describes a plasma etching apparatus utilizing plasma confinement. The plasma etching apparatus includes confinement rings that comprise quartz rings that are positioned to surround an interaction space between two electrodes of the apparatus where a plasma is formed during operation of the apparatus. The dimensions of the slots are chosen to insure that charged particles of spent gases in the plasma exiting the interaction space are neutralized by wall collisions as they exit the slots. Two voltage sources of different frequencies are used to apply voltages to the electrodes in a fashion that isolates each source from the other. The other Lenz U.S. Pat. No. 6,019,060 disclosure describes the use of confinement rings in which the confinement rings are raised and lowered to facilitate workpiece transport.
An illustrative example of a plasma processing chamber having confinement rings is shown in FIG. 1. The Figure shows a cross-sectional view of the plasma processing chamber 100 having confinement rings 102a and 102b. Although only two confinement rings are shown, it should be understood that any number of confinement rings may be provided. Within plasma processing chamber 100, there is shown a first electrode 104, representing the workpiece holder on which a workpiece 106 is positioned during etching. The first electrode 104 may be implemented by any suitable chucking system, e.g. electrostatic, mechanical, clamping, vacuum, or the like, and is surrounded by an insulator 108. During etching, RF power supply 110 may generate RF power having a frequency of about 2 MHz to about 27 MHz to first electrode 104.
Above workpiece 106, there is disposed a second upper electrode 112, which is coupled to a reactor top formed of a conductive material such as aluminum. The reactor top is coupled to confinement rings 102. Second upper electrode 112 is electrically insulated from grounded chamber wall 116 by insulator 118 and is powered by an RF power supply 120 to facilitate the formation of a plasma out of etchant source gases supplied via a gas line (not shown). RF power supply 120 may have any suitable frequency, such as 2 MHz to 27 MHz. It shall be appreciated by those skilled in the art that the plasma processing chamber of FIG. 1 represents a capacitively coupled plasma processing chamber although the confinement rings also operate well with other types of processing chambers such as inductively coupled plasma processing chambers.
Other approaches for confining plasma include magnetic confinement. The U.S. Pat. No. 5,767,628 and U.S. Pat. No. 5,936,352 both use magnetic confinement to generate a partially confined plasma and are hereby incorporated by reference.
Keller et al. in U.S. Pat. No. 5,767,628 discloses a processing apparatus including a chamber, an induction coil for providing a RF induced electromagnetic field to generate a plasma, and a plurality of magnetic dipoles that produce a confined plasma within the processing chamber.
Samukawa et al. in U.S. Pat. No. 5,936,352 discloses a processing apparatus that includes a plasma chamber having a first set and a second set of parallel electromagnetic elements. An oscillating energy having a first phase is applied to the first set of parallel electromagnetic elements. Another oscillating energy having an opposite phase is applied to the second set of parallel electromagnetic elements to produce oppositely moving energy fields in the processing chamber such that electrons are confined in a plasma produced in the chamber.
In spite of the well-known method for confining plasma either partially or fully, a novel system and method for generating confined plasma is needed. This need is caused by the semiconductor industry shifting from 200 mm wafers to 300 mm wafers. The 300 mm wafer occupies more than twice the area of the 200 mm wafer. As a result of the 300 mm wafer being larger, the operating conditions for semiconductor fabrication change substantially. Prior art methods for generating a confined plasma that worked for 200 mm wafer do not work on 300 mm wafers due to the higher gas flows and higher radio frequency (RF) power levels.
Therefore it would be beneficial to provide an apparatus that generates a confined plasma that occupies a substantially larger volume.
Additionally, it would be beneficial to provide an apparatus that confines plasma in processing chamber that operates using high gas flows.
It would also be beneficial to provide an apparatus that confines plasma in a processing chamber that operates with high RF power levels.
Furthermore, it would be beneficial to provide a method for generating a confined plasma in a processing chamber that operates using high gas flows.
Further still, it would be beneficial to provide a method for generating a confined plasma in a processing chamber that operates using high RF power levels.
The present invention includes a system and method for confining plasma using a plasma processing apparatus. The plasma processing apparatus comprises a first electrode, at least one power generator, a second electrode, at least one confinement ring, and a ground extension for draining charge from the plasma boundaries. The first electrode is configured to receive a workpiece and has an associated first electrode area. The power generator is operatively coupled to the first electrode, and the power generator is configured to generate an RF power that is communicated to the first electrode. The second electrode is disposed at a distance from the first electrode. The second electrode is configured to provide a complete electrical circuit for RF power communicated from the first electrode. Additionally, the second electrode has a second electrode area that may vary in size from that of the first electrode area. At least one confinement ring is configured to assist in confining the plasma. The plasma is generated with the RF power being communicated between the first electrode and the second electrode. The ground extension drains charge from the plasma boundaries with a grounded conductive surface.
Additionally, the invention includes a method for generating a confined plasma in a plasma processing apparatus. The method includes providing a first electrode configured to receive a workpiece in which the first electrode has a first electrode area. Additionally, the method includes providing a second electrode disposed at a distance from the first electrode. The second electrode is configured to provide a complete electrical circuit for RF power communicated from the first electrode. Further still, the second electrode has a second electrode area that may vary in size from that of the first electrode area. The method then provides for the engaging of a power supply to communicate a plurality of electrical charge from the first electrode and the second electrode. The method also provides for the draining of the plurality of charge at a plasma boundary. The plasma boundary provides a perimeter for the confined plasma.